Dasar Pemrograman JavaPertemuan 2Pemrograman Berbasis ObyekOleh Tita Karlita

Topik:Membedakan antara valid dan invalid identifiers.Mengetahui Java technology keywords.Mengetahui 8 tipe data primitif.Mendefinisikan literal value untuk tipe data numerik dan tekstual.Mendefinisikan primitive dan reference variable.Mendeklarasikan variabel bertipe class.Mengetahui nilai inisialisasi default.Konversi dan casting tipe data primitif.

IdentifiersNama yang digunakan oleh programer untuk memberi nama pada variable, class, atau method.Can start with a Unicode letter, underscore (_), or dollar sign ($) Are case-sensitive and have no maximum length Examples:

1. foobar // legal2. BIGinterface // legal: embedded keywords3. // are OK.4. $incomeAfterExpenses // legal5. 3_node5 // illegal: starts with a digit6. !theCase // illegal: must start with7. // letter, $, or _

Java Keywords and Reserved Wordsare considered as reserved keywordsmay not be used as identifiers.None of the reserved words have a capital letters2 keywords that are reserved in Java but which are not used : const dan goto

abstract

do

implements

private

this

boolean

double

import

protected

throw

break

else

instanceof

public

throws

byte

extends

int

return

transient

case

false

interface

short

true

catch

final

long

static

try

char

finally

native

strictfp

void

class

float

new

super

volatile

continue

for

null

switch

while

default

if

package

synchronized

Primitive TypesThe Java programming language defines eight primitive types: Logical - boolean Textual - char Integral - byte, short, int, and long Floating - double and float

Primitive Types

Literalsis a valuecannot appear on the left side of assignments.

Logical literalsThe boolean data type has two literals, true and false. For example, the statement:

1. boolean isBig = true;2. boolean isLittle = false;Note: boolean literal tidak boleh berharga 0 atau 1

Textual LiteralsThe range: 0 ~ 216 - 1. Java characters are in Unicode character (16-bit encoding).

char literalsExpressed by enclosing the desired character in single quotes ( ).Example:char c = w;Express as a Unicode value specified using four hexadecimal digits, preceded by \uExample:char c1 = \u4567;

char literalsSpecial Characters \n for new line \r for return \t for tab \b for backspace \f for formfeed \ for single quote \ for double quote \\ for backslash

String literalsIs not a primitive data type; it is a classRepresent sequences of charactersHas its literal enclosed in double quotes ( )Example:String s = Characters in strings are 16-bit Unicode.;String s = Good Morning !! \n;

Integral literals byte, short, int and longExpressed in decimal, octal, or hexadecimal.2 The decimal value is 2 077 The leading 0 indicates an octal value 0xBAAC The leading 0x indicates a hexadecimal value

Has a default type of int

Specify a long integer by putting an 'L' or 'l' after the number. 'L' is preferred as it cannot be confused with the digit '1'. Example:long x = 25L;

Integral

Floating-Point literalsFloating point literal includes either a decimal point or one of the following:E or e (add exponential value)F or f (float)D or d (double)3.14 a simple floating point value (a double) 6.02E23 a large floating point value 2.718F a simple float size value 123.4E306D a large double valueDefault is doubleSpecify a float by putting an F' or f' after the number. Example:float x = 2.5F;

Note:Semua tipe data primitif yang numerik (selain char dan boolean) adalah signed.

Member Variables Initialization

Reference variable

Conversion of primitivesTerjadi pada saat kompile.Conversion of a primitives bisa terjadi pada:AssignmentMethod callArithmetic promotion

Primitive Conversion: AssignmentTerjadi ketika suatu nilai kita berikan pada suatu variabel yang tipe datanya berbeda dari data aslinya.Tipe data yang baru harus mempunyai ukuran lebih besar dari tipe data yang lama.

1. int i;2. double d;3. i = 10;4. d = i; // Assign an int value to a double variable

Nilai d = 10.0

Primitive Conversion: AssignmentContoh konversi yang illegal

1. double d;2. short s;3. d = 1.2345;4. s = d; // Assign a double to a short variable

Muncul error: possible loss of precisionKarena tipe data short lebih kecil dari double.

Aturan untuk primitive assignment conversionBoolean tidak bisa di konversi ke tipe data lainNon-boolean dapat di konversi ke tipe data lain selain boolean, konversi yang dilakukan adalah widening conversion

Note: widening conversion adalah merubah tipe data suatu variabel ke tipe data yang ukuran bit nya lebih besar dari aslinya.

Javas widening conversionsFrom a byte to a short, an int, a long, a float, or a doubleFrom a short to an int, a long, a float, or a doubleFrom a char to an int, a long, a float, or a doubleFrom an int to a long, a float, or a doubleFrom a long to a float or a doubleFrom a float to a double

Note: Konversi antar primitive types yang tidak mengikuti arah panah disebut dengan narrowing conversion.

Javas narrowing conversionsFrom a byte to a charFrom a short to a byte or a charFrom a char to a byte or a shortFrom an int to a byte, a short, or a charFrom a long to a byte, a short, a char, or an intFrom a float to a byte, a short, a char, an int, or a longFrom a double to a byte, a short, a char an int, a long, or a floatNote: Ubah arah panah!!

Primitive Conversion: AssignmentAda yang istimewa tentang integral literal assignment

Ilegal : 1.234 adalah literal untuk double sehingga tidak bisa di berikan pada float.float f = 1.234;

Legal: khusus untuk integral literal aturan assignment conversion dibebaskan.byte b = 1;short s = 2;char c = 3;

Illegal: Pembebasan assignment conversion untuk integral literal hanya untuk assigment terhadap nilai.int i = 12;byte b = i; i adalah bukan nilai

Primitive Conversion: Method CallTerjadi ketika kita berusaha melewatkan suatu nilai variabel sebagai argumen suatu method, dimana tipe data variabel method tersebut berbeda dengan yang diterima.

1. float frads;2. double d;3. frads = 2.34567f;4. d = Math.cos(frads); // Pass float to method // that expects double

Hint: Math.cos(double d);Pada contoh diatas frands yang bertipe float akan secara otomatis di konversi menjadi double.Pada contoh diatas terjadi widening conversions.

Primitive Conversion: Method CallNarrowing conversions tidak diperbolehkanContoh ilegal:

double d = 12.0; Object ob = myVector.elementAt(d);

Hint : myVector.elementAt(int i);Hasil kompile: Incompatible type for method.Harus dilakukan casting secara eksplisit untuk mengkonversi dari double ke int

Primitive Conversion: Arithmetic PromotionTerjadi pada operasi matematika.Kompiler berusaha mencari tipe data yang sesuai dengan tipe data operan yang berbeda-beda.

1. short s = 9;2. int i = 10;3. float f = 11.1f;4. double d = 12.2;5. if ((s * i) >= (f/d))6. System.out.println(>>>>);7. else8. System.out.println(

Aturan: Arithmatic PromotionUnary operators: +, -, ++, --, ~

Jika operan bertipe byte, short, atau char, maka dikonversikan ke int

Aturan: Arithmatic PromotionBinary operators: +, -, *, /, %, >>, >>>,

Primitives and CastingCasting means explicitly telling Java to make a conversion.Cara: tambahkan tipe data yang diinginkan dalam tanda kurung sebelum nilai.

1. int i = 5;2. double d = (double)i;

Sama dengan:

1. int i = 5;2. double d = i;

Primitives and CastingAre required when you want to perform a narrowing conversion.

1. short s = 259;2. byte b = s; // Compile error3. System.out.println(s = + s + , b = + b);Pesan error = Explicit cast needed to convert short to byte.

Solusi: dengan menambahkan casting1. short s = 259;2. byte b = (byte)s; // Explicit cast3. System.out.println(b = + b);

Hasil : b = 3Kenapa 259 = 1 0000 0011The cast tells the compiler Yes, I really want to do it

true, false, null reserved wordconst, goto is keyword not in used